BMT Standards questions

In looking at the pictures and in my memory, there were a few variations of the standards. First was with the roof lines, some had vents that protruded from the roof and some had louvered vents that were flush when closed. Second was with the route signs. On some there appear to be louvers over the signs and they are smaller, others are larger and unobstructed. I also see that the numbers on the sides varied too.

Is there any listing of numbers, any reason for the changes?

Also, there were some that were rebuilt, correct? Which ones, when, and were some of the things noted above a result of the rebuild? nycsubway.org doesn't have any explanation that I could find. Any other place to look?